In the prior art many corrosion protective coating systems are disclosed and many of those corrosion protective coating systems are commercialised. Although various systems may have certain advantages over others, most of them have serious drawbacks. Common corrosion protecting systems comprise coating systems, optionally comprising various layers of materials, shrink sleeves, and tapes, optionally provided with adhesive layers, and combinations of such systems.
U.S. Pat. No. 5,817,413 and its Continuation-In-Part U.S. Pat. No. 6,033,776, both of Scapa Tapes North America, for example, disclose a high shear pipeline tape comprising a backing material having on one surface thereof a rubber-based adhesive layer. The rubber-based adhesive layer comprises a rubber mix and a tackifying resin. The rubber mix comprises crosslinked halogenated rubber, non-crosslinked rubber and a styrenic blockpolymer or terpolymer, e.g. a Kraton® polymer. The non-crosslinked rubber is preferably butyl rubber, preferably a mixture of virgin butyl rubber and recycled butyl rubber (butyl rubber is a copolymers of about 98 wt. % isobutene and 2 wt. % isoprene). The tackifying resin is used to provide the desired adhesiveness to the rubber mix and may be selected from a very large group of materials, e.g. rosins, modified rosins, rosin esters, polymerised petroleum hydrocarbons, polymerised terpenes and various resins. Examples 1 and 2 disclose formulations comprising different tackifiers, e.g. Endex® 155 (an aromatic hydrocarbon resin available from Eastman Chemical Company, Indopol® H-100 (an isobutene/1-butene copolymer having a number average molecular weight of about 910, formally available from British Petroleum Chemicals, but currently available from e.g. Amoco Chemical Company and Innovene), Escorez® 1102 (an aliphatic hydrocarbon resin having an average molecular weight of about 1300, available from ExxonMobil), and Piccopale® 100 (a polyterpene resin). Escorez® 1102 is made by polymerising petroleum fractions having a boiling point from about 15° C. to about 410° C. at atmospheric pressure which are formed by the thermal cracking of petroleum feedstock. The fractions may be polymerised thermally or in the presence of a catalyst, for example a Friedel-Crafts catalyst such as AlCl3. Usually the petroleum feedstock, e.g. light naphtha, heavy naphtha, kerosene, gas oil, vacuum gas oil and comprising C5 olefins and diolefins, C6 olefins and diolefins or a mixture of C5 and C6 olefines and diolefins, is cracked in the presence of steam. The products from this cracking process usually have a boiling point of −15° C. to 280° C. and may comprise about 30 to 60% olefins, 10 to 30% diolefins, 20 to 50% aromatics and 5 to 20% paraffins and naphthalenes. Preferably the product is subjected to fractionation to remove C2 to C4 light ends, thermal soaking and distillation to remove hydrocarbons such as cyclic diolefins including cyclopentadiene and methyl cyclopentadiene as dimers (cf. U.S. Pat. No. 4,690,958). Consequently, Escorez ® 1102 and 1315 (see below) are not isobutene based polymers. The high shear tape according to U.S. Pat. Nos. 5,817,413 and 6,033,776 is suitable as a pipe wrap system, provided that the pipe is coated with a primer. Example 3 discloses the use of Escorez® 1315, a hydrocarbon resin having a number average molecular weight of about 950. However, this high shear pipeline tape has a number of disadvantages. First of all, it is required that a bare metal pipe if first coated with a liquid primer, preferably comprising a rubber and a tackifying resin. Secondly, the rubber-based adhesive layer of the tape comprises significant amounts of crosslinked material which is known to be detrimental for the self-healing properties of the rubber-based adhesive layer.
WO 00/52381 of Raychem Ltd. discloses a further shrink sleeve for sealing a welding joint of insulated pipes, wherein between the end portions of the sleeve and the edges of the insulation a sealant or an adhesive is applied. The adhesive may be a polyamide based hot melt adhesive formulation. The sealant is preferably a blend of atactic polypropylene and polyisobutene, optionally with a tackfier, although other products are expressly said to be acceptable as well (cf. page 5, lines 15-17). The nature of the atactic polypropylene and the polyisobutene and their ratio is not disclosed.
CA A 2.308.802 of Shaw Industries, Ltd., discloses a heat-shrinkable polyolefin shrink sleeve that can be applied on the bare welding joints of polypropylene coated pipelines. Polypropylene coatings which usually consist of a combination of epoxy/adhesive/polypropylene, are used for high temperature pipelines. For applying such a heat-shrinkable polyolefin shrink sleeve to the welding joints of the polypropylene coated pipes, an adhesive is necessary to bond the end edges of the shrink sleeve to the end edges of the propylene coatings to ensure a proper seal. However, common high strength adhesives used for this purpose suffer from the disadvantage that they usually bond well to the polyolefin shrink sleeve, but not to the propylene coating. On the other hand, other adhesives that do bond well to the polyolefin shrink sleeve as well as to the polypropylene coating, i.e. low strength mastic compositions, suffer from the disadvantage that they have insufficient shear resistance, in particular at elevated temperatures. CA A 2.308.802 therefore proposes to employ a two-component system for applying a heat-shrinkable polyolefin shrink sleeve to polypropylene coated pipelines. This two-component system comprises a functional coating (indicated by the reference number 21) and a bonding agent (indicated by the reference numbers 22 and 23). The functional coating adheres very well to the bare surface of the joint of the steel pipeline, but does not adhere to the polypropylene coating. On the other hand, the bonding agent, which is applied between the edges of the functional coating and the propylene coating as can be seen in e.g. FIG. 2, adheres well to both coatings and provides a, although weak, water-resistant bond between the shrink sleeve and the polypropylene coating. The functional coating may be a mastic composition, a hot melt adhesive or a hybrid thereof, whereas the bonding agent is preferably a mastic composition. The mastic composition may comprise amorphous material or synthetic polymers or mixtures thereof. Examples of typical mastic compositions that are disclosed in CA A 2.308.802 are blends of substantially amorphous materials, e.g. butyl rubber, natural rubber and latex SBR rubber, and tackifying resins, e.g. synthetic hydrocarbon tackifying resins, rosin ester tackifying resins and inert fillers such as calcium carbonate, talc and carbon black. These mastic compositions may further comprise other amorphous materials or synthetic polymers, e.g. asphalt, polybutene and amorphous polyolefins, e.g. amorphous polypropylene, styrene-isoprene copolymers and liquid butyl polymers. Obviously, the protective system disclosed in CA A 2.308.802 is highly complex and requires many different types of materials. Moreover, shrink sleeves in general suffer from the disadvantage that they do not have self-healing properties.
U.S. Pat. No. 6,355,318 of Shawcor Ltd. also discloses a shrink sleeve based system for protecting welding joints of pre-isolated pipes. In the field, pre-isolated pipes are connected by welding the service pipe that extends beyond the insulation material, where after the welded joint is insulated encased by a shrink sleeve. An important requirement of such a shrink sleeve as already explained above is that it provides a water-tight connection and mechanical protection to the insulation and therefore should adhere very well to the insulation as well as to the pipe. To that end, an adhesive composition is applied between the edges of the insulation material and of the shrink sleeve. The nature of the adhesive composition is irrelevant since it may be selected from a wide range of materials, e.g. a sealant, a mastic or an hot melt adhesive. Obviously, this system suffers from the same disadvantages as the system disclosed in CA A 2.308.802.
U.S. Pat. No. 6,589,346 of Bredero-Shaw Company discusses the technical problems encountered with protecting steel pipes and tubing for underground installation against corrosion. The usual method involves sandblasting the surface of the steel pipe, coating said surface with an epoxy coating and covering it with a polyolefin jacketing material like HDPE or PP. In particular with small diameter pipes, it is difficult to provide a uniform coating of the epoxy coating. Secondly, using a tape as jacketing material, wherein the tape is spirally wound around the pipes, provides weak joints at the area of overlap and poor coverage of radial or longitudinal welding joints. Furthermore, spirally wrapped jacketing material is said to cause poor low temperature adhesion of the epoxy coating to the pipe.
U.S. Pat. Nos. 6,465,547, 6,569,915 and 6,794,453, all of Shawcor Ltd., disclose coating or insulating crosslinked polypropylene compositions. U.S. Pat. No. 6,465,547 expressly discloses in column 1, lines 50-54, that polymers in which the predominant chain units comprise propylene or a higher olefin such as butene tend to depolymerise when exposed to free radicals to effect crosslinking. These patents are typically directed to crosslinked materials and heat-shrinkable articles made thereof.
Another shrink sleeve system is disclosed in US 2004/0028862 to Burwell et al. In particular, this patent application is directed to joining and sealing overlapping edges of heat shrinkable polymeric wrap-around sleeves. Such sleeves comprise an outer layer of heat shrinkable polyolefin material and an inner layer of an adhesive, which adheres the sleeve to the substrate. The sleeve is wrapped around the welding joint of a pipeline, subsequently heated to cause shrinkage of the sleeve. Prior to the heat shrinking step, the overlapping edges of the sleeve are covered by a patch to prevent slippage of the overlapping ends during heat shrinking and subsequent creeping of the overlap joint. The invention disclosed in US 2004/0028862 is a patch comprising a dimensionally stable heat resistant fibrous backing layer and a layer of a high shear strength pressure sensitive adhesive which comprises a layer selected from the group consisting of isobutene polymers such as polyisobutene, polybutene and butyl rubber (butyl rubber is an elastomeric polymer based on about 98% isobutene and 2% isoprene and can easily be crosslinked as is well known in the art). It is expressly said that it is preferred that these materials are at least partially crosslinked to increase shear strength. Other preferred adhesive materials are silicones. Additionally, the nature or the properties of the polyisobutene are not disclosed.
US 2004/0191515 to Mullen, discloses an improved pipe coating for in particular subsea pipelines for the transportation of crude oil. Usually, such coatings consist of a protective epoxy-based protective coating that is applied on the steel pipe which is then covered with a marine concrete layer. The improved coating comprises a layer of polypropylene or polyethylene copolymer mixed with a polypropylene or polyethylene sintered material which is applied between the epoxy-based protective coating and the marine concrete layer to enhance shear resistance of the coating system.
Commercial processes to produce pre-coated steel pipes are very complex and are environmentally unfriendly. First of all, the surface of the steel pipes must be thoroughly cleaned by sandblasting and treatment with acids such as phosphoric acid and chromate. The steel pipe is then heated to a particular material. Subsequently, a primer is applied, usually an epoxy coating. Further layers to improve the protection can be applied, e.g. polyolefin coatings or layers having at least one surface thereof coated with an adhesive composition.
Other corrosion protective systems are based on compositions comprising non-crosslinked material. For example, U.S. Pat. No. 5,898,044 and US 2006175578 of Frans Nooren Afdichtingssystemen B. V. disclose a composition comprising an apolar, non-setting fluid polymer having a glass transition temperature lower than −60° C., wherein the polymer has a surface tension of less than 40 mN/m above the glass transition temperature and one or more fillers.
The corrosion protective coating systems disclosed in the prior art are in particular hampered by the fact that many materials are used or even have to be used that lack a good compatibility. Often, adhesive systems must be used that adhere very well to some materials, but not to others, with the consequence that even different adhesive systems must be used within the same corrosion protective coating system. There is therefore a need in the art for an adhesive composition that is widely applicable and has an excellent compatibility with the common materials used in corrosion protective coating systems and with the materials used for the construction of the pipes, pipelines and the like, e.g. steel, metal and concrete.